The calorie differential is so small, it really doesn't matter. Drinking it the way you like it best, makes the most sense.

It's true, in theory that cold water would have a "negative" calorie balance because you'd have to burn additional calories to maintain body temperature, but I remember in college a human biology professor had us calculate how much weight you could lose (in theory) just with this change. I don't remember the specific results, but it was something ridiculously low like 3-4 lb per year (assuming 1 gallon of ice water consumed per day).

He went on to further debunk, talking about ways in which the "real math" was probably even less (such as the reduction in body temperature, could increase hunger.... stuff like that).

I always knew it was ridiculously small, if even any effect, but shoot...even if it's half a pound every 5 years, I"ll take it!!

I prefer my water room temperature and in one of my special water bottles that have straws. I have two, one at work and one at home. I'm a freak about my water... One day, at work, I lost my water bottle and I tweaked! But crisis averted, I found it in the garbage. The janitors are required to throw them away. Now I have my name and work phone # on it with a sharpie.

I always knew it was ridiculously small, if even any effect, but shoot...even if it's half a pound every 5 years, I"ll take it!!

If it were proven to have even that much effect, you'd probably be right. There've been no studies (to my knowledge) that prove it helps at all. And it could actually hurt weight loss (at least according to the college biology professor).

He told us that drinking quite a bit of cold water every day could reduce a person's body temperature at least temporarily (maybe longer). At a reduced body temperature, your metabolism slows, as it takes fewer calories to maintain a lower body temp. In essence you could be shooting yourself in the foot. You could be decreasing the calories in AND the calories out part of the equation.

It's also possible (and also not proven) that drinking very cold water could increase your appetite, making it harder to stick to your planned calories.

Also, the body has to work to maintain body temperature - so drinking very hot liquids also could "burn" more calories than drinking liquids at room temperature. In cold weather, drinking hot beverages would aid the body in maintaining body temp and in hot weather, drinking cold water would aid in maintaining body temp (that is saving you calories - which you don't want to do if you want to lose weight).

One student asked whether that meant that a person should drink hot beverages in hot weather, and cold beverages in cold weather to maximize calorie expenditures. In theory, that could work (no proof here either), but that just sounds terribly unpleasant to me. I don't want to drink hot beverages in hot weather. And if I'm cold, I don't want an ice-cold beverage either.

The point the biology professor left us with, is that none of these theories are proven, but there's just as much scientific rationale for cold water decreasiong metabolism as there is for it increasing metabolism. It's possible that drinking cold water has no effect, and it's just as possible that it would have a detrimental as an advantageous effect.

Because none of these theories have been proven, and all have their scientific arguments it still makes sense to drink water at the temperature that you like.